Resins such as thermoplastic materials may be used in various applications. For applications in which external forces are exerted on a resin structure, it is desirable that the resin structure be reinforced with fibers such as fiberglass. Reinforcing a resin structure in this way desirably increases the resistance of the resin structure to such external forces. Moreover, fiber reinforcement of resin is beneficial because it more easily allows the resin to be cut and formed into pellets or other similar structures after the resin solidifies.
A conventional scheme for reinforcing a resin with fibers generally entails drawing a continuous bundle or roving of fibers into a molded die, wetting the fibers with molten resin within the die, extruding the wetted fibers from the die, and cooling the extruded fibers to form solidified and reinforced resin structures. These resin structures may then be cut into pellets of desired size for any of various uses, including injection molding. Other more specific uses are described in U.S. Pat. No. 5,268,050, which is incorporated herein by reference.
When a roving of fibers is wetted with molten resin, it is desirable that the molten resin uniformly impregnate the fibers in the roving. That is, not only should the molten resin coat the external surface of the roving, but the resin should also be evenly distributed and interspersed between individual fibers in the roving. Uniform impregnation maximizes reinforcement of the resin structure and yields the most desirable physical properties of such structure. If uniform impregnation is not achieved during the wetting stage, it is likely that fibers in the resulting resin structure will be in physical contact with one another and, hence, free to abrade upon one another. Such physical contact coupled with abrasion may reduce the life of the resulting resin structure, especially when impacted by external forces. Moreover, cutting the resin structure into pellets would simply expose the fiberglass core, so the impact strength of the pellets would be further minimized, if not entirely negated.
Various processes exist for resin reinforcement with fibers, and various processes have been suggested for achieving a thorough impregnation of fibers with molten resin. For example, in U.S. Pat. No. 4,728,387, Hilakos suggests loosening a roving of fibers by passing the roving through tension bars or rolls before or during wetting of the fibers with molten resin. Also, it has been suggested that a roving of fibers may be loosened by passing the fibers through a series of baffles or deflection units, as described by Amaike et al. in U.S. Pat. No. 5,658,513 and by Augustin et al. in U.S. Pat. No. 5,277,566. Glemet et al. provides a similar teaching in U.S. Pat. No. 4,957,422 and U.S. Pat. No. 4,937,028. All four of these patents are incorporated herein by reference.
Notwithstanding the multitude of resin impregnation schemes proposed in the art, achieving a homogeneous distribution of molten resin between and around individual fibers in a roving, as well as removing air trapped between the individual fibers, persist as problems faced by the skilled artisan in achieving reinforced resins with the most desirable physical properties.